https://devzone.nordicsemi.com/f/nordic-q-a/10034/can-host-send-message-to-device-by-using-gzllHi: I develop my project with gazell, Device can keep send to host,but host can&#39;t keep send to device(I&#39;m not mean for host sent ack to device). In my program, I use &quot;nrf_gzll_add_packet_to_tx_fifo&quot; in while(1) of host,and I use &quot;nrf_gzll_fetch_packet_from_rx_fifoen-USTelligent Community 13Tue, 03 Nov 2015 11:20:14 GMThttps://devzone.nordicsemi.com/thread/37193?ContentTypeID=1Tue, 03 Nov 2015 11:20:14 GMT137ad170-7792-4731-bb38-c0d22fbe4515:0f163ed9-ee6b-49d4-ac01-fcab41460a9echenyu<p>Thank you ! I know.</p><div style="clear:both;"></div>https://devzone.nordicsemi.com/thread/37192?ContentTypeID=1Tue, 03 Nov 2015 10:24:45 GMT137ad170-7792-4731-bb38-c0d22fbe4515:ac4f8ba3-4b74-45d9-9b5e-16c7351496aePetter Myhre<p>The Host in a Gazell network is always listening, and it is the Device that always initiates a communication. Each packet that a Device sends is required to be acknowledged by the Host. It is possible for the Host to send data to the Device by piggybacking data to an acknowledgement (ACK) packet. Therefore a Host has to wait for a packet from a Device before it can send any data to it.</p><div style="clear:both;"></div>